This invention concerns piston pumps, and more particularly, those having a delivery ranging from some liters/minute up to several liters/minute. Such pumps are particularly used in the so-called waterblasters, i.e., those equipments which produce a jet water under pressure, possibly mixed with chemical detergents, to be directed on the object to be washed through a lance.
The above-mentioned pumps are of the fixed flow type and usually have two or three ceramic plungers.
The connecting rod/crankshaft assembly is usually made of anti-friction material. Each piston is provided with two automatic valves, one for the suction, and one for the delivery. Usually the pumps marketed are provided with some accessories, particularly, a control unit of the pump, separate from the latter.
This control unit connected to the delivery port of the pump enables to increase or decrease the flow from the lance, which is connected to the control unit by a flexible hose. The variation of the flow is obtained by deviating to a return line a part of the flow entering the control unit.
The control unit also enables to interrupt, while the pumps are working, the flow coming out from the lance by deviating it completely to the return line.
The above control unit is made in such a way that when closing the flow coming out from the lance, not only does the flow go to the return line, but the pressure is strongly reduced (for example, from 1500-3000 psi to 60-70 psi), the pump, therefore, works no-load.
There are pumps of this type, having more than two plungers, even opposed.
Furthermore, there are pumps incorporating the above-mentioned control unit so as to obtain an assembly (pump plus control unit) to simplify the assembling job.
The known pumping units above all those with two plungers are provided with a pressure damping device on the pressure line. This pressure damping device is an independent component of the pump and connected to it by a high-pressure hose, and its function is to make uniform the outlet pressure and avoid cyclical peaks. This pressure damping device also has the function of a pressure accumulator. It therefore gives back the energy received during the pressure peak.
As this pressure damping device is independent from the pump, specialized manpower is required to mount it on waterblasters or similar equipment and to connect it to the pump pressure line, the effects of which on costs are significant.
There are, however, some pumping units of the above type with two or three plunger pumps that also incorporate the pressure damper and, consequently, an easier assembling job.
In such a way besides the time saving due to the fact of installing just one unit, there is also the advantage of eliminating all the high-pressure connectors among the pump, the control unit and pressure damper, and a significant time saving on installation is therefore obtained. Moreover, all possible leakages due to connectors are eliminated.